[88BlueTSiQuest]

A little more info.

Generally with a 7.1 system, you should follow the THX guidelines for speakers. This would have you installing Bipole speakers on the sides and rear of the system, to further 'blur' the soundstage, and eliminate your ability to pin point the source of sound.

DTS seems to play on the actual directionality, so direct radiating speakers all the way around are a nice choice. But you can still choose to set it up in the THX fashion.

If you are totally happy with your current speakers, but would like to get into a 7.1 environment, you could simply consider going with another center channel speaker like you currently have, and pick up any 7.1 receiver. As I stated in my previous reply, most 7.1 receivers are capable of driving a single rear speaker, and since the actual surround backs are monaural, you wouldn't lose any sound to the missing speaker.

If you have a DTS capable DVD player, you might find the 6.1 surround a better mix anyways, as I tend to find that most DTS encoded movies are generally louder, and have more effects than the Dolby mixes. Besides, the fact that DTS actually uses the 6th speaker as an independant channel, vs. Dolby using 'tricks' to make you think they are independant.